Levan is a naturally occurring fructan polysaccharide produced by certain bacteria, characterized by its β-2,6-linked D-fructofuranose backbone with β-2,1 branches. This unique structure confers high solubility and film-forming capabilities. Levan has attracted increasing attention as a microbial polysaccharide with biomedical potential, comparable to alginate and dextran in terms of versatility and functionality.
Molecular Structure
Levan consists primarily of linear chains of D-fructofuranose units linked by β-(2→6) glycosidic bonds, with branching occurring at β-(2→1) positions. This architecture promotes a compact, spherical conformation in aqueous solution. The molecular weight typically ranges from 10 to 100 million Da, depending on the producing microbial strain and fermentation conditions. A branching degree of approximately 10–15% enhances molecular flexibility and water-holding capacity compared to linear fructans such as inulin.
Production and Properties
Levan is biosynthesized by levansucrase enzymes produced by microorganisms including Bacillus subtilis, Gluconobacter, and Zymomonas mobilis, using sucrose as both carbon source and polymerization primer. It exhibits exceptional water solubility (>100 g/L at room temperature), thermal stability up to 60°C, biodegradability, non-toxicity, and prebiotic activity through selective fermentation by gut microbiota. Levan forms viscous solutions and can self-assemble into nanoparticles. However, its applications may be limited by reduced chemical stability under acidic conditions and the complexity of downstream purification processes.
Biomedical Applications
In biomedical and cosmetic fields, levan functions as an effective skin moisturizer and anti-irritant due to its humectant properties. Chemically modified derivatives, such as sulfated levan, demonstrate antiviral (including anti-HIV), anticoagulant, and anti-inflammatory activities. In drug delivery systems, levan is employed in the development of nanocarriers, hydrogels, and controlled-release emulsions. Additionally, its ability to support cell proliferation makes it suitable for wound healing applications, nutraceutical formulations, tissue engineering scaffolds, and immunomodulatory therapies.
